The general goal of this project is to further understand the regulation and function of the gene products that form the recently discovered epithelial Na channel. the context in which these studies are undertaken relates to the pathogenesis of salt-sensitive hypertension. There are 2 subprojects. The first subproject capitalizes on new information indicating that primary cultures of the renal inner medullary collecting duct from salt-sensitive rates transport substantially more Nathan do these cells cultured from salt-resistant rats. The hypothesis derived from this data is that an abnormality in the epithelial Na channel complex, or in associated regulatory molecules, contributes to the pathogenesis of salt- sensitive hypertension in humans. the experiments are directed at 3 specific aims. The first aim is to determine the effect of physiologic maneuvers known to alter the activity of collecting duct Na transport on the messenger RNA and protein of each of the 3 major subunits. The focus will be on the kidney and uroepithelium, but responses in lung and colon will be measured in order to examine tissue heterogeneity. The second aim is to determine the biophysical properties of the epithelial Na channel as it exists in the apical membrane of inner medullary collecting duct cells from salt- sensitive and salt-resistant rats. the third aim is to determine the effect of overexpressing one or more of the epithelial Nachannel subunits in the inner medullary collecting duct on Na transport. Using transgenic mice, the rate-limiting subunit will be selectively overexpressed and the animals examined for their salt-sensitivity. These experiments will test the hypothesis that an overactive Na channel in the inner medullary collecting duct will contribute to salt-sensitive hypertension. The second subproject is based on the new observation that the uroepithelium contains epithelial Nachannel subunits. The experiments proposed in this portion will test the hypothesis that these subunits serve a different function that they do in the collecting duct. Rather than participate in Na reabsorption, the hypothesis is that they participate in activation of mechanosensitive nerve fibers. In the renal pelvis, afferent nerve activity is markedly activated by an increase in renal pelvic pressure. Preliminary data suggest that the epithelial Nachannel subunits participate in this activity. the specific aims are to determine the mechanisms by which ameliorate modulates the activation of afferent renal nerve activity. to determine the extent to which ameliorate inhibits the release of putative mediators of mechanoreceptor activation, and to determine the effect of elimination of one of the subunits in genetically altered mice on the activation of afferent renal nerve activity. These experiments will test a novel hypothesis which may have important implications for an interaction of Na channel function and the central nervous system.